All-wheel drive vehicles may have a primary full time driveline and a secondary part-time driveline, where the secondary driveline provides additional traction under vehicle acceleration or poor traction conditions. A torque coupling may be used in the secondary driveline to limit the torque flow from the primary driveline and to allow for differences in speed between the primary and secondary drivelines. When the secondary driveline is not providing additional traction it continues to rotate and energy is lost overcoming friction and spin loss (oil churning), both of which act to reduce fuel economy. To improve fuel economy, it is desirable to automatically disconnect the secondary driveline to eliminate energy losses.
It would be advantageous to develop a rear wheel drive unit having a twin side shaft torque coupling which may be selectively engaged to increase an efficiency of and to provide additional traction to a driveline where the rear wheel drive unit is incorporated.